Catalyst components for the polymerization of olefins

Details Catalyst components for the polymerization of olefins Catalyst components for the polymerization of olefins

2002-06-10

2004-11-30

Choi, Ling-Siu (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S142000, C526S124300, C526S123100, C526S107000, C502S103000, C502S115000, C502S127000

Reexamination Certificate

active

06825309

ABSTRACT:

The present invention relates to catalyst components for the polymerization of olefins, in particular propylene, comprising a Mg dihalide based support on which are deposited a Ti compound having at least one Ti-halogen bond and at least two electron donor compounds selected from specific classes. The present invention further relates to the catalysts obtained from said components and to their use in processes for the polymerization of olefins. The catalysts of the present invention are able to give, with high yields, propylene homopolymers characterized by high xylene insolubility, a broad range of isotacticity and, in particular conditions by a very high content of stereoblocks.
Catalyst components for the stereospecific polymerization of olefins are widely known in the art. The most largely widespread family of catalyst systems comprises a solid catalyst component, constituted by a magnesium dihalide on which are supported a titanium compound and an internal electron donor compound, used in combination with an Al-alkyl compound. Conventionally however, when a higher crystallinity of the polymer is required, also an external-donor (for example an alkylalkoxysilane) is needed in order to obtain higher isotacticity. One of the preferred classes of internal donors is constituted by the esters of phthalic acid, diisobutylphthalate being the most used. This catalyst system is capable to give very good performances in terms of activity, isotacticity and xylene insolubility provided that an external electron donor compound is used. When the external donor is missing, low yields, low xylene insolubility and poor isotacticity are obtained. On the other hand, when the external donor is used, high xylene insolubility is obtained only together with a high isotacticity. Moreover, the Molecular Weight Distribution (MWD) is, under the normal single step polymerization conditions, not broad (Polydispersity Index in the range 3.6-4.5). These characteristics, although useful in certain applications, are not desirable in certain other fields such as the production of bi-oriented polypropylene films (BOPP). For application in this field in fact, polypropylenes are required to have a broad MWD (Polydispersity Index higher than 5) a lower flexural modulus (obtainable by lowering crystallinity of the polymer) while at the same time retaining a high xylene insolubility. Moreover, it has been found that suitable polymers for application in this field are those that, in addition to the above requirements, have also a comparatively high content of the so called stereoblocks, i.e., of polymer fractions which, although predominantly isotactic, contain a not negligible amount of non-isotatctic sequences of propylene units. In the conventional fractionation techniques such as the TREF (Temperature Rising Elution Temperature) those fractions are eluted at temperatures lower than those are necessary for the more isotactic fractions. In EP 658577 is described a method for producing PP homopolymers having a high stereoblock content. It comprises polymerizing propylene in the presence of a catalyst comprising (i) a solid catalyst component in which a Ti compound and diisobutyl phthalate are supported on a MgCl
2
, (ii) an Al-alkyl compound as a co-catalyst and (iii) a 3,3,3,trifluropropyl(alkyl)dimethoxysilane as external donor. In example 1 it can be seen that although the polymerization is carried out in two sequential steps under different conditions, the MWD of the bimodal polymer obtained is not sufficiently broad (Polydispersity Index 4.7). Furthermore, the bimodal polymers can have problems of homogeneity due to presence of distinct fractions with pronounced difference in average Mw. In said example 1 the weight percentage of stereoblock fraction measured via TREF, on the polymer after visbreaking, is about 31%, while in another run (in Table 2) the amount of stereoblock fraction was about 26%. In view of the above, it would be desirable to have a catalyst component with still improved characteristics and in particular capable to give polymers with high xylene insolubility, high stereoblock content and broad MWD suitable for making the polymers usable in the BOPP sector.
It has now unexpectedly been found a catalyst component having the above advantages which comprises Mg, Ti, halogen and two electron donor compounds selected from specific classes. It is therefore an object of the present invention a catalyst component for the polymerization of olefins CH
2
═CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, comprising Mg, Ti, halogen and at least two electron donor compounds, said catalyst component being characterized by the fact that at least one of the electron donor compounds, which is present in an amount from 15 to 50% by mol with respect to the total amount of donors, is selected from esters of succinic acids which are not extractable, under the conditions described below, for more than 20% by mol and at least another electron donor compound which is extractable, under the same conditions, for more than 30% by mol.
According to the present invention, the esters of succinic acids not extractable for more than 20% by mol will be defined as non-extractable succinates. The electron donor compounds extractable for more than 30% by mol will be defined as extractable electron donor compounds. Preferably, the amount of non-extractable succinates is between 20 and 45 and more preferably from 22 to 40% by mol with respect to the total amount of the electron donor compounds.
In a preferred embodiment is used a succinate which is not extractable for more than 15% and another electron donor compound which is extractable for more than 35%.
Among the non-extractable succinates mentioned above, particularly preferred are the succinates of formula (I) below
in which C* is an asymetric carbon, the radicals R
1
and R
2
, equal to, or different from each other, are a C
1
-C
20
linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms; and the radicals R
3
and R
4
, equal to, or different from each other, are C
1
-C
20
alkyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms with the proviso that at least one of them is a branched alkyl; said compounds being, with respect to the two asymmetric carbon atoms identified in the structure of formula (I), stereoisomers of the type (S,R) or (R,S) that are present in pure forms or in mixtures.
R
1
and R
2
are preferably C
1
-C
8
alkyl, cycloalkyl, aryl, arylalkyl and alkylaryl groups. Particularly preferred are the compounds in which R
1
and R
2
are selected from primary alkyls and in particular branched primary alkyls. Examples of suitable R
1
and R
2
groups are methyl, ethyl, n-propyl, n-butyl, isobutyl, neopentyl, 2-ethylhexyl. Particularly preferred are ethyl, isobutyl, and neopentyl.
Particularly preferred are the compounds in which the R
3
and/or R
4
radicals are secondary alkyls like isopropyl, sec-butyl, 2-pentyl, 3-pentyl or cycloakyls like cyclohexyl, cyclopentyl, cyclohexylmethyl.
Examples of the above-mentioned compounds are the (S,R) (S,R) forms pure or in mixture, optionally in racemic form, of diethyl 2,3-bis(trimethylsilyl)succinate, diethyl 2,3-bis(2-ethylbutyl)succinate, diethyl 2,3-dibenzylsuccinate, diethyl 2,3-diisopropylsuccinate, diisobutyl 2,3-diisopropylsuccinate, diethyl 2,3-bis(cyclohexylmethyl)succinate, diethyl 2,3-diisobutylsuccinate, diethyl 2,3-dineopentylsuccinate, diethyl 2,3-dicyclopentylsuccinate, diethyl 2,3-dicyclohexylsuccinate.
Among the extractable electron donor compounds particularly preferred are the esters of mono or dicarboxylic organic acids such as benzoates, malonates, phthalates and succinates. Among malonates particularly preferred are those of formula (II):
where R
1
is H or a C
1
-C
20
linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, R
2
is a C
1
-C
20
linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, R
3
and R
4
,e

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